(1) Field of the Invention
The present invention relates to a processing method and a processing apparatus for electronic parts.
(2) Description of the Related Art
The flow method using solder reflow is a widely known method for soldering electronic parts on a printed circuit board. As a typical example of electronic parts, a method for soldering a coil shall be explained.
FIG. 1 shows an outline diagram of a coil 1. The coil 1 is made of a coil bobbin 2, a coil section 3, and sections 4 which serve as terminal sections after undergoing a subsequent process. The coil section 3 is wound around the bobbin 2 by using a coil winder, or the like. In general, a conductor wire making up the coil section 3 is a coated wire in which the surface of a wire rod having copper as a principal constituent is coated with a resin. Polyurethanes, imides, polyesters, and the like, are used as the resin, and the coated wire is commonly referred to as enamel wire.
As shown in FIG. 2, solder plating 36 are formed on the terminals. This process shall be discussed in detail later.
As shown in FIG. 3, such a coil is mounted on a printed circuit board 20. The terminal section is inserted in a through-hole provided in the printed circuit board 20, and by processing with a solder reflow apparatus, the solder plating 36 of the terminal section and a land 21 are soldered together. The solder reflow apparatus shall be discussed later.
The process for plating the terminal with solder shall be explained with reference to FIG. 4 to FIG. 8. As shown in FIG. 4, the section 4 which serves as the terminal section takes the form of a coated wire in which the surface of a wire rod 9 having copper as a principal constituent is coated with a resin 10. Furthermore, a leaded solder 38 (lead content 95%) is prepared in a molten state (400° C.) inside a solder plating tank 37. Next, as shown in FIG. 5, by immersing the section which serves as the terminal section into the solder plating tank 37, the coating resin 10 peels off due to heat and turns into enamel particles 39 which melt in the solder 38. Next, as shown in FIG. 6, when the section which serves as the terminal section is lifted out of the solder plating tank 37, the solder plating 36 bonds onto the terminal section.
As another form of a coil, there exists a coil having terminal posts. FIG. 7 shows an outline diagram of such a coil. Coil wire is wound around a coil bobbin 2 to form a coil section 3. A section 41 serving as a terminal section is wound a number of times around a terminal post 40 protruding from the coil bobbin 2. When the terminal post 40 is immersed in the solder plating tank, in a plating process such as that discussed using FIG. 4 to FIG. 6, solder plating bonds to the terminal post 40. FIG. 8 shows a cross-section of the terminal post 40 onto which solder plating has bonded. The solder plating bonds onto the periphery of the terminal post 40, and the wire rod 9 whose resin coating has been removed is integrated with the terminal post 40 via the solder plating 36.
Next, the operation of the solder reflow apparatus shall be discussed with reference to FIG. 19.
A commonly known solder reflow apparatus solders by conveying, in a predetermined direction, a board on which surface mount components without leads and discreet components with leads are placed together, while supplying such a board with molten solder shot out from a nozzle. In this type of solder reflow apparatus, the following are sequentially placed along a board conveyance direction A: a flux application apparatus 23 for applying flux onto the board 20 and a part to be soldered; a preheating apparatus 24 made of a panel heater, or the like, for preheating the part to be soldered and the board 20 in order to properly dry the flux; and a molten solder supply unit 25 for supplying molten solder onto the board 20 and the part to be soldered. The board 20 is conveyed by a conveyor 26 which holds both sides of the board 20 firmly in place and accompanies the board 20 along a conveyor path 27.
The molten solder supply unit 25 includes a primary jet nozzle 28 for properly supplying molten solder onto the entire soldering surface of the board 20 that is placed with an electronic part, and a secondary jet nozzle 29 for removing excess molten solder from the solder supplied board 20. The jet nozzles 28 and 29 are immersed within a solder dip tank 30 filled with molten solder. This type of solder reflow apparatus is explained in detail in Japanese Laid-Open Patent Application No. 2000-357865 Publication.
At the same time, plasma cleaning technology for cleaning a terminal section of a device has come into recent use. An example of this is discussed in Japanese Laid-Open Patent Application No. 2002-28597 Publication. Japanese Laid-Open Patent Application No. 2002-28597 Publication discusses the case where the terminal section of a liquid crystal display device is processed. FIG. 9 shows a liquid crystal display 42 which is made by joining a pair of boards 43 made of a transparent glass sheet or plastic film placed one on top of the other, via a frame-shaped sealant (not shown), and enclosing liquid crystal within the space enclosed by both boards 43 and the sealant. One edge of one board 43 protrudes outside one edge of the other board 43, and the inner surface of this protruding portion serves as a terminal section 44 where a terminal 45, which is made of a plurality of transparent conductive films such as ITO, is laid out. In the terminal section 44, for example, flexibly structured drive circuit boards are joined via an anisotropic conductive adhesive. During this time, if the terminal section 44 is contaminated with a foreign substance such as dust or residue, a defective mechanical attachment or defective electrical connection arises in the joint.
Accordingly, by using a plasma irradiator 46 to irradiate the surface of the terminal section 44 with a stream of gas which is converted to plasma, cleaning is carried out either by blowing off the foreign substance adhering to the surface of the terminal section 44, or by weakening the chemical bonding strength acting in the foreign substance and separating the foreign substance from the surface, or by chemically decomposing the foreign substance per se and eliminating it from the surface of the terminal section 44. The plasma irradiator 46 is made of a nozzle cylinder 47 serving as an anode, and a torch (not shown) serving as a cathode, provided within the nozzle cylinder 47. The head of the nozzle cylinder 47 is a tapered-tip irradiation port 47a. During cleaning, an arc discharge arises between the anode nozzle cylinder 47 and the cathode torch while a reaction gas such as air (atmospheric air), nitrogen gas (N2), or argon (Ar) is supplied in the nozzle cylinder 47. Accordingly, the reaction gas inside the nozzle cylinder 47 is heated and ionized to become ions and electrons forming the plasma state. The reaction gas that has been converted to plasma irradiates the surface of the terminal section 44 by being jetted out as a plasma jet 48 from the nozzle cylinder's 47 irradiation port 47a, which has a spot diameter of 5 mm. At this time, a liquid crystal display device 42 is, for example, placed on a moving table 49, and the plasma irradiator 46 is maintained on a fixed position above the moving table 49. The plasma jet 48 is jetted out onto the surface of the terminal section 44 from the irradiation port 47a of the nozzle cylinder 47, while the moving table 49 is moved together with the liquid crystal display device 42, at a fixed speed along a lengthwise direction of the terminal section 44. With this, the contaminants are removed and the entire surface of the terminal section 44 is cleaned up to a clean state by sequentially applying the plasma jet 48 to all the areas of the surface of the terminal section 44 and blowing off the contaminants in these areas, or weakening the chemical bonding strength acting in the contaminant and thereby separating it from the surface, or chemically decomposing the contaminant per se.
Subsequently, a circuit board is bonded on top of the terminal section 44 via an anisotropic conductive adhesive. As the surface of the terminal section 44 is in a clean state in which contaminants have been removed, it is possible to maintain a satisfactory bonding condition and bond the circuit board to the terminal section 44.
However, the problem of not being able to handle lead-free soldering, in consideration of the environment, exists in the conventional example of electronic parts processing.
In the solder plating process for the terminal section explained with reference to FIG. 4 to FIG. 8, when leaded solder is replaced with lead-free solder, the solder cannot be plated properly onto the terminal section. Compared with leaded solder, the melting point of lead-free solder is high, and a high temperature is needed to maintain molten lead-free solder in the solder plating tank. Furthermore, lead, which makes mixed crystallization with copper easy, is not included. Accordingly, although the coating resin peels off when the coated wire of the section serving as a terminal section is immersed in the molten solder, the wire rod oxidizes and the solder does not bond to the wire rod. Alternatively, in the case of a small wire diameter of φ0.1 mm or less, the portion from which the resin has been peeled breaks off due to thermal stress generated in the wire rod, and the section serving as the terminal section, as a matter of fact, dissipates in the solder plating tank.
Due to these circumstances, processing using leaded solder is unavoidably carried out on the terminal section of the coil. However, in this case, the lead from the leaded solder of the terminal section melts into the solder dip tank in the solder reflow apparatus which solders coils onto printed circuit boards, and the lead content in the solder within the solder dip tank gradually increases. In the lead-free soldering process, there is a need to manage the lead content in the solder which is used. Generally, a standard of less than 1% is used, with standards such as less than 0.3% and less than 0.2% being used in stricter operations.
However, when lead mixes in, as described above, it is necessary to maintain the management standard for lead content by totally replacing the solder in the solder dip tank every few days or weeks of operating the solder reflow apparatus, thereby posing a big burden.
Moreover, the plasma cleaning technology introduced in Japanese Laid-Open Patent Application No. 2002-28597 Publication is, first and foremost, a processing technology for cleaning a terminal section which is an exposed conductive section, and absolutely no discussion is made regarding the handling of lead-free solders.
In view of the existing problem, the objects of the present invention are to provide electronic parts having a terminal section plated with lead-free solder, a processing method and processing apparatus for plating lead-free solder onto the terminal section of an electronic part, and a processing method and processing apparatus for adapting an electronic part to a lead-free soldering process.